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We can divide the list into 4 elements: the first 10 as a, the next 10 as b, the next 10 as c, and the last 10 as d
From the relations we are given, we can form the equations: 

Adding the first two equations, we get a + 2(b + c) + d = 300,000
We can substitute the value of a + d as 100,000 to get b + c as 100,000
Using this value in the first and second equation would give a and d as 20,000 and 80,000, respectively.
We are told that the average of the first 10 employees increases by 100%, that is, it changes from 20,000 to 40,000
The average of the last 10 increases by 200%; that is, it changes from 80,000 to 240,000
The total of all the four elements would be 40,000 + 100,000 + 240.000 = 380,000
Giving the average to be 38000/4 = 95000